#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
#include <unordered_set>
#include <random>
#include <cassert>
#include <fstream>
#include <utility>
#include <functional>
#include <time.h>
#include <stack>
#include <array>
#define popcount __builtin_popcount
using namespace std;
using ll=long long;
typedef pair<int, int> P;

int main()
{
    int n; cin>>n;
    int m; ll c; cin>>m>>c;
    ll a[100010], b[100010];
    for(int i=0; i<n; i++){
        cin>>a[i];
    }
    for(int i=0; i<m; i++){
        cin>>b[i];
    }
    //sort(a, a+n);
    sort(b, b+m);
    ll cnt=0;
    for(int i=0; i<n; i++){
        int t=upper_bound(b, b+m, c/a[i])-b;
        cnt+=m-t;
    }
    printf("%.7lf\n", (double)cnt/(double)n/(double)m);
    return 0;
}